Dark matter is a type of matter, whose composition is unknown and which corresponds to 80% of the matter in the universe. Its name refers to the fact it does not emit or interact with any type of electromagnetic radiation, being completely transparent throughout the electromagnetic spectrum.
However, it interacts with the known matter through <u>gravity</u>.
In this sense, it is believed that the Milky Way has 90% dark matter and only 10% ordinary matter (known matter). Because, like gravity, dark matter can not be observed directly, however its existence is inferred through the movement of the stars and the cosmic dust within the galaxy.
The revolving nosepiece is one of the parts of a microscope, used for holding the objective lenses. They can be turned to put a particular objective lens in place to be used in order to vary magnification.
